In cardiopulmonary bypass operations, a patient's circulatory system is linked to a heart-lung machine to permit the extracorporeal circulation of blood. In these surgical procedures, a bypass circuit is created where venous blood bypasses the heart and is reintroduced into an artery. Also, cardiotomy blood is scavenged from the surgical site, combined with the venous blood, and reintroduced into the patient. The extracorporeal bypass circuit performs numerous functions, including removing emboli and particulate matter entrained in the blood, regulating the carbon dioxide and oxygen content of the blood, and regulating the blood temperature.
In the past, venous blood was filtered and collected in a venous reservoir and the cardiotomy blood was filtered and collected in a cardiotomy reservoir. Work in this art area has included efforts to simplify and improve these systems, as, for example, providing combined venous and cardiotomy reservoir systems. Other work has been directed to simplifying and improving the blood storage, filtration, and defoaming systems for both venous and cardiotomy blood.
In some systems, a sealed venous reservoir is used. This allows a vacuum to be pulled in the reservoir for the purpose of assisting the removal of blood from the patient. However, using such sealed systems creates a potential problem. During the surgical procedure, it is possible to develop either over-or under-pressure situations within the sealed reservoir. Either situation can lead to undesirable consequences for the patient. Therefore, it is known to use safety valves which can regulate the pressure within the sealed reservoir so that it does not exceed acceptable positive and negative pressure limits.
Safety valves include unidirectional valves such as umbrella valves and duck-bill valves. A unidirectional valve permits the escape of air when there is a positive or negative air pressure within the reservoir. Umbrella valves typically are used to vent negative pressure in a reservoir. Duck-bill valves typically are used to vent positive pressure. This valve includes two tips or flaps and an integral base defining a generally cylindrical opening. The tips or flaps butt against each other preventing the passage of air in or out of the reservoir, responding to positive pressure within the reservoir by spreading apart. Duck-bill valves in current use typically are comprised of silicone materials which are engineered to respond to certain pressures, thus allowing fluid to flow through the valve at desired pressures.
We have discovered that the tips or flaps of duck-bill valves used as air outlet valves in blood reservoirs can adhere together after long periods of time or after exposure to adverse environmental conditions. Typically such valves comprise silicone. This self-adhesion is an extremely undesirable situation, as a non-functioning valve can produce a build-up of pressure in a venous reservoir, resulting in reverse blood flow. Thus, a need exists to prevent the self-adhesion of duck-bill valve tips when the duck bill valve is used as a safety valve in blood reservoirs.